1. Field of the Invention
Exemplary embodiments of the present invention relate to an apparatus and method for transmitting and receiving data; and, more particularly, to an apparatus and method for transmitting and receiving data for a wireless communication system.
2. Description of Related Art
In general, a communication system is categorized to a wired communication system and a wireless communication system. In case Of the wired communication system, a terminal and a network are connected through a wired link and stably transmit and receive data in a high speed. However, the wired communication system has a limitation in user mobility. In case of the wireless communication system, a terminal and a network transmit data using a predetermined frequency. Accordingly, a data transmit rate is slower than that of the wired communication system. However, there is no limitation in user mobility.
Due to rapid progress in a wireless communication technology, packet based high speed wireless communication systems have been introduced lately. Further, there have been many studies and researches made to develop various methods for transmitting data further efficiently and more quickly. In general, methods for controlling a transmission power adaptively to a channel state have been used to improve a packet transmit rate in a wireless communication system. However, there is a limitation to improve the packet transmit rate only using such methods. Therefore, there have been demands for developing methods for improving a packet transmit rate.
Lately, many studies have been made to develop methods for improving a packet transmit rate using various schemes. In general, a wireless communication system is divided into a physical layer (PHY) and a Medium Access Control (MAC) layer. In the PHY layer, a complex technology is used to improve reliability of transferring information and a data transmit rate.
In order to configure an ultra wideband wireless communication system, a high speed wireless transmission technology using a MIMO OFDM high speed wireless transmission technology, a channel coding method, and a high order modulation scheme have been employed at the PHY layer. In the MAC layer, a protocol for proving a high quality service to a user is defined, such as a Block Ack scheme and an Aggregation mode scheme for providing high throughput. In the aggregation mode, a plurality of packets are aggregated to one long packet in order to transmit the plurality of packets at once by transmitting the long aggregation packet at once.
For example, International Double Balanced Standard IEEE 802.11n introduces a 64-QAM high order modulation scheme and a channel coding method having a high coding rate such as a 5/6 code rate into a PHY layer. Further, IEEE 802.11n increases a data transmit rate up to 300 Mbps at a PHY layer by applying a multiple antennas OFDM modulation scheme. Further, as a standard, IEEE 802.11n selects a technology for sustaining throughput up to about 200 Mbps of a data transmit rate at a MAC layer using a Block Ack scheme and an Aggregation mode at a MAC layer in order to reduce an overhead generated due to a gap between a header and a frame.
It is possible to achieve high throughput theoretically by employing a Block Ack scheme and an Aggregation mode as standard in IEEE. However, such a high throughput cannot be achieved in a real wireless environment. In the Double Balanced Transmission scheme, a signal is transmitted with 64 QAM modulation scheme and a 5/6 code rate through multiple antennas. Comparatively, a channel may become unstable during a long packet period because a required SNR is not sustained for the long packet period at a receiver end. Also, small error propagation is required to achieve high throughput at a receiver end in a WLAN system.